High molecular weight polymers are generally incompatible with each other. When two different polymers are mixed, the blend exhibits poor mechanical properties, e.g., tensile strength or ultimate elongation. A pair of polymers is seldom sufficiently compatible to give a blend exhibiting mechanical properties as good as the weakest polymer. However, when two polymers are compatible the resulting blend can exhibit a valuable combination of properties, i.e., in addition to good mechanical properties, the blends may also exhibit favorable characteristics, such as temperature and solvent resistance of the individual polymers.